1. Field of the Invention
The present invention relates to an antenna structure provided in a headset and suitable for receiving a near-field-communication signal, and to a headset having the antenna structure.
2. Description of the Related Art
A currently available wireless headset device receives sound data, music data, or the like, sent from a sound device such as a portable telephone using near-field communication, with an antenna in the headset fitted to the ears, and plays back the received data with speakers in the headset. As an example of an antenna of a headset, Japanese Unexamined Patent Application Publication No. 2002-111352 discloses a dipole antenna in which a pair of conductor patterns each having a feeding terminal at one end is provided along the outer periphery of an arch-shaped dielectric substrate.
FIGS. 6A and 6B are a plan view and a back view of a known substrate having an inverted F-shaped pattern antenna, respectively. In a headset to be worn on the ears, a dielectric substrate 100 has a substantially circular shape conforming to the shape of a speaker-containing unit. A surface to be provided with an antenna (FIG. 6A) and the back surface (FIG. 6B) are covered with copper foil sheets 101a and 101b, respectively, for disposing circuit components. The copper foil sheet 101a covering the surface to be provided with the antenna of the dielectric substrate 100 is partially removed over a certain width to provide a region 102 for accommodating an inverted F-shaped antenna, and an inverted F-shaped conductor pattern 103 is formed thereon. A feeding portion 104 of the conductor pattern 103 is connected to a feeding line (not shown), and a grounding portion 105 is connected to a part of the copper foil sheet 101a that functions as a ground. Similarly, the copper foil sheet 101b covering the back surface of the dielectric substrate 100 is partially removed over a portion overlapping the region 102 to provide a region 106 for accommodating the inverted F-shaped antenna. As described above, in the case of a pattern antenna provided on a dielectric substrate, the copper foil sheets 101a and 101b are partially removed from both surfaces of the dielectric substrate 100 to provide a region for accommodating the antenna.
However, because the copper foil sheets 101a and 101b need to be partially removed to provide the regions 102 and 106 for accommodating the pattern antenna, the circuit components cannot be disposed on the regions 102 and 106. Therefore, the substrate needs to be enlarged to compensate for the regions 102 and 106.
Further, when the headset is fitted to human ears, because the copper foil sheets are removed from the regions for accommodating the pattern antenna, nothing shields the antenna electromagnetically from a human body in these regions. Therefore, antenna properties change when the antenna is located near a human body or the like situations.